RESUMO
Botrytis cinerea, Rhizoctonia solani and Hemileia vastatrix are three species of phytopathogenic fungi behind major crop losses worldwide. These have been selected as target models for testing the fungicide potential of a series of bis(ylidene) cyclohexanones. Although some compounds of this chemical class are known to have inhibitory activity against human pathogens, they have never been explored for the control of phytopathogens until now. In the present work, bis(ylidene) cyclohexanones were synthesized through simple, fast and low-cost base- or acid-catalyzed aldol condensation reaction and tested in vitro against B. cinerea, R. solani and H. vastatrix. bis(pyridylmethylene) cyclohexanones showed the highest activity against the target fungi. When tested at 200 nmol per mycelial plug against R. solani., these compounds completely inhibited the mycelial growth, and the most active bis(pyridylmethylene) cyclohexanone compound had an IC50 of 155.5 nmol plug-1. Additionally, bis(pyridylmethylene) cyclohexanones completely inhibited urediniospore germination of H. vastatrix, at 125 µmol L-1. The most active bis(pyridylmethylene) cyclohexanone had an IC50 value of 4.8 µmol L-1, which was estimated as approximately 2.6 times lower than that found for the copper oxychloride-based fungicide, used as control. Additionally, these substances had a low cytotoxicity against the mammalian Vero cell line. Finally, in silico calculations indicated that these compounds present physicochemical parameters regarded as suitable for agrochemicals. Bis(ylidene) cyclohexanones may constitute promising candidates for the development of novel antifungal agents for the control of relevant fungal diseases in agriculture.
Assuntos
Antifúngicos , Fungicidas Industriais , Humanos , Cicloexanonas , Doenças das Plantas/microbiologia , Fungos , PlantasRESUMO
Diseases incited by soilborne fungi are responsible for reducing the yield and cause significant impact to almost all crops. Among then, Rhizoctonia solani AG-4 is considered the most important in the cotton, common bean and soybean crops in Brazil. The use of diagrammatic scale or rating scales, as a tool to help in the quantification of the severity of a particular disease, is more common for foliar diseases. Considering the lack of a standardized, illustrated and easy-to-apply methodology for assessing the severity of R. solani lesions in cotton, soybean and common bean seedlings, a simple and precise rating scale was developed with the objective to fill this gap. The proposed scale shows four levels of disease severity, with the descriptions and illustrations for each type of lesion observed in the cotton, soybean and common bean seedlings. This developed scale was validated in many experiments and proved to be adequate for severity assessments of R. solani lesions on cotton, soybean and common bean seedlings.
Doenças causadas por fungos de solo reduzem a produtividade e impactam de forma significativa quase todas as culturas. Dentre elas, Rhizoctonia solani AG-4 é considerada a mais importante nas culturas de algodão, feijão e soja no Brasil. A utilização de escalas diagramáticas ou escalas de notas, como ferramenta para auxiliar na quantificação da severidade de uma determinada doença, é mais comum quando se trata de doenças foliares. Considerando a inexistência, até então, de metodologia padronizada, ilustrada e de fácil aplicação para a avaliação da severidade de lesões de R. solani em plântulas de algodão, soja e feijão, desenvolveu-se uma escala de notas, simples e precisa, com o objetivo de suprir essa lacuna. A escala proposta apresenta quatro níveis de severidade de doença, com descrições e ilustrações para cada tipo de lesão observada nas plântulas de algodão, soja e feijão. Essa escala foi validade em inúmeros experimentos, provando ser adequada para a avaliação da severidade de lesões de R. solani nas plântulas de algodão, soja e feijão
Assuntos
Rhizoctonia , Glycine max , Gossypium , FabaceaeRESUMO
BACKGROUND: Use of fungicide seed treatments for control of soybean soilborne diseases such as Pythium damping-off has increased worldwide. However, emergence of Pythium strains resistant to metalaxyl-M has prompted the need for alternative technologies to fungicides for damping-off control. The use of phosphites (Phis) has been proposed as a method to control oomycetes, but their use as seed treatments in soybean is limited by the lack of information on their efficacy. The effect of potassium (K) and manganese (Mn) Phis (as seed treatments) in the control of Pythium damping-off in soybean was evaluated in vitro and in vivo. In vitro, treated seeds and a control were placed on potato dextrose agar and the damping-off severity caused by Pythium aphanidermatum (Edson) Fitzpatrick, Pythium irregulare Buisman, and Pythium ultimum Trow was assessed 5 days after incubation using an ordinal scale. In vivo, treated seeds and a control were planted in polystyrene pots and emergence was evaluated 21 days after planting. RESULTS: Analysis of the in vitro data using a multinomial generalized linear model showed that the probabilities of non-germinated, dead seeds ranged from 0.64 to 1.00 in the control and from 0 to 0.13 in the Phi treatments in each of the Pythium species. Probabilities of seed germination without or with damping-off symptoms were significantly higher for seeds treated with the Phi products than for the control. In the in vivo experiment, the Phi-based products increased seedling emergence by up to 29% on average compared with the untreated control. CONCLUSION: Mn and K Phis are feasible alternatives as seed treatments to control Pythium damping-off in soybean. This study is the first, worldwide, to document the efficacy of K and Mn Phis in the control of soybean Pythium damping-off. © 2017 Society of Chemical Industry.
Assuntos
Fungicidas Industriais/farmacologia , Fosfitos/farmacologia , Doenças das Plantas/prevenção & controle , Pythium/efeitos dos fármacos , Manganês/farmacologia , Compostos de Potássio/farmacologia , Glycine max/microbiologiaRESUMO
Species in the genus Calonectria (Hypocreales) represent an important group of plant pathogenic fungi that cause serious losses to plant crops in tropical and subtropical climates. Calonectria leaf blight is currently one of the main impediments to Eucalyptus cultivation in Brazil, and various species of Calonectria have been associated with this disease. Since most previous identifications were solely based on morphological characters, much of the published literature needs to be re-evaluated. The aim of this study was thus to identify and determine the phylogenetic relationships among species that occur in the Eucalyptus growing regions of Brazil by using partial sequences of the ß-tubulin, calmodulin, translation elongation factor 1-α and histone H3 gene regions. Based on extensive collections from soil and infected eucalypt leaf samples from plantations, phylogenetic inference revealed the Ca. pteridis complex to be the most common species complex present in Eucalyptus plantations in Brazil. By elucidating taxa in the Ca. pteridis, Ca. cylindrospora and Ca. candelabra species complexes, 20 novel Calonectria species were identified, and a new name in Calonectria provided for Cylindrocladium macrosporum as Ca. pseudopteridis.
RESUMO
The objective of this study was to evaluate the effect of salicylic acid concentrations (SA) in the induction of resistance of tipping cucumber seedlings and in vitro control of Pythium sp. The treatment of cucumber seeds was carried out using SA soaking solution for 5 min at concentrations of 0 (distilled water), 0.5, 1.0, 1.5, and 2.0 mM. They were then sown in trays containing Plantmax Florestal® substrate sterilized and inoculated with Pythium sp. The experiment was conducted for 14 days in a growth chamber with controlled temperature (23 C ± 2 C), light (photoperiod of 12 hours) and relative humidity (70% ± 10%). We evaluated the percentage of seedling emergence, percentage of tipping, seedling length, and fresh weight. The levels of the enzymes phenylalanine ammonia lyase (PAL), -1,3-glucanase and chitinase were also quantified. In the experiment in vitro, SA was incorporated into the PDA (Potato, Dextrose and Agar) and we measured the mycelial growth of Pythium sp. The treatment of cucumber seeds with concentrations above 1 mM SA reduces the incidence of seedling damping-off caused by Pythium sp., however, it was not possible to discover enzymes related to the induction of resistance. The SA has no effect on the mycelial growth of Pythium sp. in vitro.
Objetivou-se neste trabalho avaliar o efeito de concentrações de ácido salicílico (AS) na indução de resistência ao tombamento de plântulas de pepino e no controle in vitro de Pythium sp. O tratamento das sementes de pepino foi realizado com imersão em solução de AS por 5 min nas concentrações de 0 (água destilada); 0,5; 1,0; 1,5 e 2,0 mM. Em seguida foram semeadas em bandejas contendo o substrato Plantmax Florestal® previamente esterilizado e inoculado com Pythium sp. O experimento foi conduzido por 14 dias em câmara de cultivo com controle de temperatura (23 oC ± 2 C), luminosidade (fotoperíodo de 12 horas) e umidade relativa (70% ± 10%). Foram avaliadas a porcentagem de emergência de plântulas, porcentagem de tombamento, comprimento de plântula e massa da matéria fresca. Foi também quantificado os teores das enzimas fenilalanina amônia-liase (FAL), -1,3-glucanase e quitinases. No experimento in vitro o AS foi incorporado ao meio BDA (Batata-Dextrose e Agar) e avaliado o crescimento micelial de Pythium sp. O tratamento de sementes de pepino com concentrações acima de 1 mM de AS reduz a incidência de tombamento de plântulas causado por Pythium sp., no entanto, não foi possível associar com enzimas relacionadas a indução de resistência. O AS não apresenta efeito sobre o crescimento micelial de Pythium sp. in vitro.
Assuntos
Cucumis sativus/imunologia , Cucumis sativus/microbiologia , Pythium , Ácido Salicílico/administração & dosagemRESUMO
The objective of this study was to evaluate the effect of salicylic acid concentrations (SA) in the induction of resistance of tipping cucumber seedlings and in vitro control of Pythium sp. The treatment of cucumber seeds was carried out using SA soaking solution for 5 min at concentrations of 0 (distilled water), 0.5, 1.0, 1.5, and 2.0 mM. They were then sown in trays containing Plantmax Florestal® substrate sterilized and inoculated with Pythium sp. The experiment was conducted for 14 days in a growth chamber with controlled temperature (23 C ± 2 C), light (photoperiod of 12 hours) and relative humidity (70% ± 10%). We evaluated the percentage of seedling emergence, percentage of tipping, seedling length, and fresh weight. The levels of the enzymes phenylalanine ammonia lyase (PAL), -1,3-glucanase and chitinase were also quantified. In the experiment in vitro, SA was incorporated into the PDA (Potato, Dextrose and Agar) and we measured the mycelial growth of Pythium sp. The treatment of cucumber seeds with concentrations above 1 mM SA reduces the incidence of seedling damping-off caused by Pythium sp., however, it was not possible to discover enzymes related to the induction of resistance. The SA has no effect on the mycelial growth of Pythium sp. in vitro.(AU)
Objetivou-se neste trabalho avaliar o efeito de concentrações de ácido salicílico (AS) na indução de resistência ao tombamento de plântulas de pepino e no controle in vitro de Pythium sp. O tratamento das sementes de pepino foi realizado com imersão em solução de AS por 5 min nas concentrações de 0 (água destilada); 0,5; 1,0; 1,5 e 2,0 mM. Em seguida foram semeadas em bandejas contendo o substrato Plantmax Florestal® previamente esterilizado e inoculado com Pythium sp. O experimento foi conduzido por 14 dias em câmara de cultivo com controle de temperatura (23 oC ± 2 C), luminosidade (fotoperíodo de 12 horas) e umidade relativa (70% ± 10%). Foram avaliadas a porcentagem de emergência de plântulas, porcentagem de tombamento, comprimento de plântula e massa da matéria fresca. Foi também quantificado os teores das enzimas fenilalanina amônia-liase (FAL), -1,3-glucanase e quitinases. No experimento in vitro o AS foi incorporado ao meio BDA (Batata-Dextrose e Agar) e avaliado o crescimento micelial de Pythium sp. O tratamento de sementes de pepino com concentrações acima de 1 mM de AS reduz a incidência de tombamento de plântulas causado por Pythium sp., no entanto, não foi possível associar com enzimas relacionadas a indução de resistência. O AS não apresenta efeito sobre o crescimento micelial de Pythium sp. in vitro.(AU)
Assuntos
Cucumis sativus/imunologia , Cucumis sativus/microbiologia , Pythium , Ácido Salicílico/administração & dosagemRESUMO
Rhizoctonia solani é um fungo causador de tombamento de plântulas em várias espécies vegetais. A quitosana é um polímero derivado do processo de desacetilação da quitina, a qual é encontrada em grande quantidade na carapaça de crustáceos, insetos e parede celular de fungos. A quitosana tem sido testada para diversos usos, inclusive no controle de fitopatógenos em agricultura, já que apresenta atividade antimicrobiana, para controle de patógenos. O presente trabalho teve como objetivo avaliar o efeito fungistático de diferentes concentrações de quitosana (0; 0,25; 0,5; 1 e 2%) no crescimento micelial do fungo R. solani in vitro. Os resultados obtidos demonstraram efeito significativo de quitosana nas diferentes concentrações utilizadas, na redução do crescimento micelial de R. solani. Observou-se também aumento do efeito fungistático da quitosana conforme o aumento da dose.
Rhizoctonia solani is a fungus that causes damping-off of seedlings in various plant species. Chitosan is a polymer derived from the process of desacetylation of chitin, which is found in large quantities in the exoskeleton of crustaceans, insects and fungal cell wall. Chitosan has been tested for various uses, including the control of plant pathogens in agriculture, since it presents antimicrobial activity to control pathogens. This study aimed to evaluate the fungistatic effect of different chitosan concentrations (0; 0.25; 0.5; 1 and 2%) in mycelial growth in vitro of the fungus R. solani. The results showed a significant effect of different concentrations of chitosan, in reduccing the mycelial growth of R. solani. It was also observed increased fungistatic effect with increasing of the concentration.
RESUMO
Rhizoctonia solani é um fungo causador de tombamento de plântulas em várias espécies vegetais. A quitosana é um polímero derivado do processo de desacetilação da quitina, a qual é encontrada em grande quantidade na carapaça de crustáceos, insetos e parede celular de fungos. A quitosana tem sido testada para diversos usos, inclusive no controle de fitopatógenos em agricultura, já que apresenta atividade antimicrobiana, para controle de patógenos. O presente trabalho teve como objetivo avaliar o efeito fungistático de diferentes concentrações de quitosana (0; 0,25; 0,5; 1 e 2%) no crescimento micelial do fungo R. solani in vitro. Os resultados obtidos demonstraram efeito significativo de quitosana nas diferentes concentrações utilizadas, na redução do crescimento micelial de R. solani. Observou-se também aumento do efeito fungistático da quitosana conforme o aumento da dose.(AU)
Rhizoctonia solani is a fungus that causes damping-off of seedlings in various plant species. Chitosan is a polymer derived from the process of desacetylation of chitin, which is found in large quantities in the exoskeleton of crustaceans, insects and fungal cell wall. Chitosan has been tested for various uses, including the control of plant pathogens in agriculture, since it presents antimicrobial activity to control pathogens. This study aimed to evaluate the fungistatic effect of different chitosan concentrations (0; 0.25; 0.5; 1 and 2%) in mycelial growth in vitro of the fungus R. solani. The results showed a significant effect of different concentrations of chitosan, in reduccing the mycelial growth of R. solani. It was also observed increased fungistatic effect with increasing of the concentration.(AU)
Assuntos
Rhizoctonia , QuitosanaRESUMO
A temperatura é importante para estudos com Rhizoctonia solani por ser um patógeno cosmopolita e polífago. Nas temperaturas adequadas o patógeno pode ser favorecido, o qual obtém sucesso no processo doença. Já em temperaturas inadequadas, o seu crescimento e desenvolvimento pode ser retardado. O objetivo foi avaliar a influência da temperatura no crescimento micelial, na produção de escleródios e na patogenicidade de isolados de R. solani. Obtiveramse 18 isolados de plântulas de algodão, oriundos dos estados de Minas Gerais (8), Bahia (3), Goiás(2), Mato Grosso (4) e Mato Grosso do Sul (1), que foram testados nas temperaturas de 15°C, 18°C, 21°C, 24°C, 27°C e 30°C. Para o crescimento micelial, os isolados foram dispostos em placas de Petri (9 cm de diâmetro), contendo meio batata-dextroseágar. As placas foram acondicionadas em câmaras de germinação com fotoperíodo de 12 horas. Realizaram-se medições ortogonais do diâmetro da colônia, diariamente, por 8 dias e quantificou-se o índice de crescimento micelial (ICM). As placas foram mantidas por três meses nas respectivas câmaras de crescimento para análise da produção de escleródios. Para a determinação de patogenicidade e a avaliação da severidade da doença, seguiu-se o método descrito por Oliveira et al. (2008). Os dados obtidos foram submetidos à analise de variância. Houve interação significativa entre isolados e temperaturas. Quanto aos oito isolados de Minas Gerais, um apresentou maior ICM a 24ºC e três a 27°C, observando-se relação com o modelo quadrático. Três isolados apresentaram melhor ajuste ao modelo linear e um não diferiu estatisticamente para as temperaturas avaliadas. Os isolados de GO apresentaram maior ICM nas temperaturas de 24°C e 27°C. Para os isolados do MT, dois tiveram ajuste ao modelo linear, enquanto os outros dois tiveram ao modelo quadrático, nas temperaturas de 21°C e 24°C. Já o isolado do MS foi ajustado ao modelo quadrático a 27°C, enquanto todos os três isolados da BA foram ajustados ao modelo linear. O maior número de escleródios foi observado nas temperaturas de 15°C e 18ºC com exceção do isolado do MS, o qual obteve o maior número a 27ºC. Verificou-se que 14 isolados (6 de MG, 2 da BA, 2 de GO, 3 de MT e 1 de MS) apresentaram maior severidade entre 24°C e 27°C, ajustandose ao modelo quadrático, enquanto três isolados (2 de MG e 1 de MT) não diferiram significativamente para as temperaturas avaliadas e apenas um isolado (BA 2 I01) ajustou-se ao modelo linear.
The temperature is important for studies of Rhizoctonia solani (Kühn), since it is a cosmopolitan and polyphagous pathogen. Appropriate temperatures can favor the pathogen, which starts the infection process. On the other hand inappropriate temperatures can impose a delay to its growth and development. The objective were evaluate the influence of temperature on mycelial growth, sclerotia production and pathogenicity of R. solani strains. In the fields were obtained 18 strains from cotton seedlings on the States of Minas Gerais-MG (8), Bahia-BA (3), Goias-GO (2), Mato Grosso-MT (4) and Mato Grosso do Sul-MS (1), which were tested at temperatures of 15°C, 18°C, 21°C, 24°C, 27°C and 30°C. For mycelial growth, strains were placed in Petri dishes (9 cm diameter) containing potato-dextrose-agar (PDA). The dishes were placed into a germination chamber with a photoperiod of 12 hours. There were orthogonal daily measurements of the diameter of the colony during 8 days and the rate of mycelial growth was quantified afterwards. The dishes were kept for three months in the respective growth chambers for the sclerotia production analysis. For the pathogenicity determination and evaluation of disease severity the method described by Oliveira et al. (2008) was followed. The data were subjected to analysis of variance. There was significant interaction between isolates and temperatures. Among the eight strains of Minas Gerais, one had a higher rate of mycelial growth at 24 ° C and three at 27 ° C, adjusting to the quadratic model. Three strains showed better fit to a linear model and did not differ statistically for the temperatures. Strains from GO had a higher rate of mycelial growth temperatures of 24°C and 27°C. Concerning about the strains from MT, two were fit to a linear model, while the other two had the quadratic model at temperatures of 21°C and 24ºC. Strains from MS was adjusted to quadratic model at 27°C, while all three strains from BA were fitted to the linear model. The largest number of sclerotia was observed at 15°C and 18°C except for MS strain, which obtained the highest number at 27ºC. It was found that 14 strains (six from MG, two from BA, two from GO, three from MT and one from MS) showed a higher severity between 24°C and 27°C, adjusting to the quadratic model, while three isolates (two from MG and one from MT) did not differ significantly for the temperatures evaluated and only one isolate (BA 2 - I01) had set better to the linear model.
Assuntos
Rhizoctonia , Temperatura , Virulência , GossypiumRESUMO
Life history and recruitment information of tropical trees in natural populations is scarce even for important commercial species. This study focused on a widely exploited Neotropical canopy species, Pachiraquinata (Malvaceae), at the southernmost, wettest limit of its natural distribution, in the Colombian Amazonia. We studied phenological patterns, seed production and natural densities; assessed the importance of seed dispersal and density-dependent effects on recruitment, using field experiments. At this seasonal forest P. quinata was overrepresented by large adult trees and had very low recruitment caused by the combination of low fruit production, high seed predation and very high seedling mortality under continuous canopies mostly due to damping off pathogens. There was no evidence of negative distance or density effects on recruitment, but a clear requirement of canopy gaps for seedling survival and growth, where pathogen incidence was drastically reduced. In spite of the strong dependence on light for survival of seedlings, seeds germinated readily in the dark. At the study site, the population of P. quinata appeared to be declining, likely because recruitment depended on the rare combination of large gap formation with the presence of reproductive trees nearby. The recruitment biology of this species makes it very vulnerable to any type of logging in natural populations. Rev. Biol. Trop. 59 (2): 921-933. Epub 2011 June 01.
Información acerca de la historia de vida y reclutamiento de poblaciones naturales de árboles tropicales es escasa, incluso para especies de alto interés comercial. Este estudio se centró en una especie de dosel altamente explotada, Pachira quinata (Malvaceae), en la zona más húmeda de su distribución geográfica, en la Amazoní a colombiana. Estudiamos sus patrones fenológicos, producción de semillas y densidades naturales, además de la importancia de la dispersión de semillas y efectos denso-dependientes en el reclutamiento natural, todo lo anterior se logró con el uso de experimentos y observaciones en el campo. En este bosque estacional, la población de P. quinata estaba dominada por grandes árboles adultos y el reclutamiento era extremadamente bajo, como consecuencia de la baja producción de frutos, alta depredación de semillas y muy alta mortalidad de plántulas bajo el bosque por infección de patógenos. No encontramos evidencia de efectos de distancia al árbol parental o densidad de semillas en el reclutamiento, pero si hallamos un evidente requerimiento de claros de luz para la supervivencia y el crecimiento de plántulas, donde la mortalidad por patógenos se reduce drásticamente. Sin embargo, a pesar de la dependencia de la luz para la supervivencia, las semillas germinan en la oscuridad. En la zona de estudio, la población de P. quinata parece estar en claro declive, probablemente porque el reclutamiento depende de la coincidencia de la formación de grandes claros con la presencia cercana de árboles reproductivos. Los requerimientos de reclutamiento de esta especie la hacen muy vulnerable a cualquier actividad extractiva de árboles adultos en poblaciones naturales.